Symptoms and appearance

The main symptom is an itchy head (caused by the louse's saliva when it removes a tiny amount of blood from the scalp), but a person can have head lice and not know it. “The gold standard for diagnosing lice is finding a live one on the head, but they can be very difficult to spot,” notes Will. They crawl fast (up to 12 inches or 30 cm per hour – that's fast if you're the size of a sesame seed!) but do not fly or jump. An adult louse can be up to 1/8 inch (3 mm) in size and is pale grey or brown. “Look on the back of the head, in a line from one ear to the other,” she suggests. Nits, or louse eggs, do not move. They are oval and tan, yellow or brown. After they hatch, the shell that is left behind is clear or grayish-white. Nits are found about a quarter-inch (one cm) from the scalp. The nits are firmly glued to the hair shaft by the adult louse. Nits are most commonly found around the nape of the neck or behind the ears, although they can be found all over the scalp.

Treatment

Shampoos and lotions. Medicated shampoos or lotions (known as pediculicides because they contain a pesticide to kill the lice) are the most common treatment. It's very important to follow the treatment directions exactly. Most will require a follow-up application seven to 10 days later.

The most common over-the-counter products contain permethrin (eg Nix and Kwell), which is the treatment of choice recommended by the AAP; or pyrethrin plus piperonyl butoxide (eg RID, A-200, R&C, Pronto and Clear Lice System) which is similar to permethrin, but should not be used by people with allergies to chrysanthemums. Scalp irritation is a common side effect. Some lice have become resistant to some pesticides. If you're pregnant or nursing, consult your doctor before using these products, and they can't be used on kids under age 2. Only treat your kids if they have lice, not as a preventative measure.

Home remedies. Some people have tried home remedies, such as covering the scalp with petroleum jelly, olive oil, mayonnaise or large amounts of conditioner in order to “smother” the lice and nits, or antiseptics like tea tree oil products, but these methods have not been evaluated by medical trials. However, a study published in the journal Pediatrics found that a scalp treatment that involved specific steps with the facial cleanser Cetaphil was effective, find details here. Never use gasoline, kerosene, pet shampoos, WD-40 or other dangerous products.

Whatever treatment you choose, you will still need to use a special fine-tooth comb (such as one called the LiceMeister) to comb through wet hair and remove all the nits. Comb every three or four days for two weeks.